Hello everyone,
I'm working on a application that uses Cassandra and has a geolocation component.
I was wondering beside the slides and video at http://www.readwriteweb.com/cloud/2011/02/video-simplegeo-cassandra.php
that simplegeo published regarding their strategy if anyone has implemented geohash storage
and search in cassandra.
The basic usage is to allow a user to find things close to a geo location based on distance
radius.
I though about a couple of approaches.
1. Have the geohashes be the keys using the Ordered partitioner and get a group of rows between
keys then store the items as columns in what it would end up looking like wide rows since
each column would point to another row in a different column family representing the item
nearby.
2. Simply store the geohash prefixes as columns and use secondary indexes to do queries such
as >= and <=.
The problem I'm facing in both cases is ordering by distance and searching neighbors.
The neighbors problem is clearly explained here: https://github.com/davetroy/geohash-js
Once the neighbors are calculated an item can be fetched with SQL similar to this.
SELECT * FROM table WHERE LEFT(geohash,6) IN ('dqcjqc', 'dqcjqf','dqcjqb','dqcjr1','dqcjq9','dqcjqd','dqcjr4','dqcjr0','dqcjq8')
Since Cassandra does not currently support OR or a IN statement with elements that are not
keys I'm not sure what the best way to implement geohashes may be.
Thanks in advance for any tips.